A technology, in which a band elimination filter is applied to a torque command value for the stabilization of a servo control system of a machine tool, has been widely used. In a general filter adjustment procedure, sine wave sweeping or square wave sweeping is performed for a speed control loop including a torque command generating unit and a speed detecting unit, so that a frequency response of the speed control loop is measured. Next, a graph visualized as a Bode diagram is closely examined, so that a resonance frequency can be seen with one's eyes. Even though the Bode diagram is not visualized, since the specification of the resonance frequency is possible, a technology for performing automatic adjustment of the band elimination filter has been designed.
Since the characteristics of the automatic adjustment do not depend on the adjustment policy or capacity of an engineer who performs manual adjustment, an adjustment result with a relatively small variation is obtained. By the automatic filter adjustment function, the stiffness of a machine tool is measured with a variation smaller than that of manual measurement.
As a method for performing the adjustment of a band elimination filter, there has been reported a method for detecting a frequency with a vibration level exceeding a threshold value in order to suppress mechanical resonance, thereby automatically performing the adjustment of a plurality of band elimination filters (for example, JP 2012-23834 A). In this related art, when two band elimination filters have center frequencies adjacent to each other, a filter width of a first filter is widened.
The aforementioned related art discloses an automatic adjustment algorithm of a plurality of band elimination filters. However, the subject of the related art is merely for performing adjustment for simply solving resonance. Actually, the related art substitutes for the adjustment of a servo control system just before machine shipment. The related art does not disclose how to cope with a secular change and an individual difference of the stiffness of a machine tool as a long-term facility or a mass-produced industrial product.